Preparation of n-dimethxl



Reissued June 21, 1949 .LS'TAT-ETS "PATENT OFFICE =:BREPARA'IION F N-DIMETHYL- ETHANOLAMINE William Gresham, Alapocas, Del., assignorto E. I. 'duPont de Nemours'and'Company,"Wil- :mington,sDel.,ia"corporation of Delaware .NoeDrawing. OriginalNo. 2,462,736, 'date'dlEbruary '22, 1949, Serial No. 548,803, 'August'fl,

-tion:of-aldehyd-e cyanhyd-rins'in the-presence of an organic solvent-andan alkylating agent.

An object of the present invention isto provide animproved-synthesis for the preparation of *w alkyl substituted-alkanolarnines from aldehyde or k'etone cyan'hydr'ins by xalkylation during 'hy -drogen'ation. Another obj e'ct is' to provide a syn- 'thesis of such allcanolamines by the liquid phase hydrogenation of "an aldehyde cyanhydrin in the presence of an alky-lating agent and an inert organic solvent. A further object'is to provide suitable reaction rconditions iand catalysts 'for conducting the synthesis. Other .objects rand "advantages of the invention will hereinafter appear.

'Thesynthesis is conducted by passing 'theicyanhydrin to'-be= alkylate'dwith hydrogen, an al.- dehyde, and a"-solvent into a reaction "zone "charged with a suitable hydrogenation catalyst. The reaction is preferablyeonducted in'a large namount er '-a"catalyst 'and an excess of an organic solvent to inhibit the formation of de- "mnnpos'ition products during' the r'ea'ction. The s reaction"may' be 'conducted'insuch'a way that contact 'between the substituted *alkanolamine produced andthe cyanhydrin is'avoided as 'much as possible.

The cyanhydrins which may be employed" inthe ssynthes'is in'clude theaaldehyde'cyanhydrins, and more particularly formaldehyde cyanhydrin, aeetal'di'ahyde, -nand-isopropanol, nand, isobutanal, and. the higher aldehyde cyan'hydrins, as=We1l as theketone-cyaiihydrins such, for example, as dimethyl, diethyl, methyl ethyl, dipropyl, methyl -propyl,'-and similar symmetrical sand unsymmetricalketone';cyanhydrins.

The alkylating agents used in accordwith the invention are the aldehydes such, for example, as formaldehyde,*a'cetaldehyde; the *propanals, butanals,i'and the higher :straight and branched 'iehaimaliphatic aldehydes. @These agents should besused in amounts governed :by the z-degreecof iialkylationa'desired, generally from 0.2 7t0-4mols rper molz-of zthe cyanhydriniissample, the higher limit being used .if N-dialkylsubstitution is desired.

Theiinert organic solvent-should for optimum r resultsT beea solvent for -the :cyanhydrinssas well as for the alkanolamines produced, but one that is not affected by the reaction, and of these the lower molecular weight oxygenated organic com- Application for "reissue April 9, 194-9,

"pounds are preferred. Examples 'of such-solvents :are alcohols, :e. g., methanol, ethanol, .n and isopropanol, and 'nand :isobutanol, which are especially 'effective' in inhibiting the decomposition of the cyanhydrins; the others, e. g. ,di-

methyl and 'diethyl ether; the .acetals ve. g.,

m thylal, dimethoxy :m'ethylether, *ethylal, and -1,3-.dioxolane and the organic :amides, -e. g. di-

'm'ethyl and 'diethyl formamide.

The presence 'of the 'aforesai'd inert'solvent in- "hibits "the formation of Ldecomposition products 'of the cyan-hydrin :employed, and consequently "assists in directing :the'course' of the reaction toward the "desired alkylated and hydrogenated product. These diluents should preferably be employed in amounts to give solutions containing 'by weight'from in the order 'of'4-to 20-parts per vli uidphase 'and- 'in-ithe presence of a suitable hydrogenation :catalyst, such, for example, as nickel, 'cobalt, fused nickel-cobalt, copper chromite catalyst, Raney nickel catalyst or other hydrogenation catalysts known to be useful in --the hydrogenation "of "nitriles 'to amines. The "reaction is carriedout atwa temperature ranging *from 25 to 200 C. and :underpressure, which, is *not criticaLand mayrbemaintained at 1 to 1000 atmospheres. 'Itz'ispreferred, however, to conduct the hydrogenation rand "alkylation of 1 these nitriles at temperatures between .r25vto -.C. and under "a pressure ibetween .200 and 700 atmospheres.

The more detailed practiceg-ofrtheinvention is i'illustrated by the accompanyin examples of "preferred embodiments :of the invention, :in 'which :parts are by Weight unless :otherwise stated:

Example 1.-A silver-lined high pressure-resisting shaker tube was charged with 7 parts of formaldehyde cyanhydrin, 7.7 parts of formaldehyde, 140 parts of methanol, and 20 parts of a nickel alloy skeleton catalyst obtained by dissolving about 85% of the aluminum, from a nickel alloy containing 48% nickel and 52% aluminum, by leaching with'an alkali. Hydrogen was introduced and the reaction conducted at a temperature between 93 and 98 C. under a pressure of 700 atmospheres for approximately 1 hour, The pressure was released and the products filtered from the catalyst and separated by fracticnal distillation. Upon analysis, it was found that 38.5% of the formaldehyde cyanhydrin had been converted to N-dimethylethanolamine and 43.7% to N-methyl diethanolamine.

Example 2.--The process of Example 1 was substantially duplicated, using '7 parts of formaldehyde, '7.8 parts of formaldehyde cyanhydrin, 140 parts of methanol, and 20 parts of the nickel catalyst. The reaction was conducted at a temperature between 94 and 99 C. for approximately 1 hour. A 46% conversion of the formaldehyde cyanhydrin to N-dimethylethanolamine and 50.7% conversion to N-methyldiethanolamine was obtained.

Example 3.The process of Example 1 was substantially duplicated, using 14 parts of formaldehyde cyanhydrin, 15.6 parts of formaldehyde, 140 parts of methanol, and 20 parts of the nickel catalyst. The reaction was conducted at a temperature between 97 and 107 C. for about 1 hour. The products obtained showed a conversion of 45.5% of the formaldehyde cyanhydrin to N-dimethylethanolamine, 6.8 parts of N- methyldiethanolamine and N-methoxymethyldiethanolamine.

Example 4.The process of Example 1 was substantially duplicated, using '7 parts or formaldehyde cyanhydrin, 7.8 parts of formaldehyde, 140 parts of methanol, and 20 parts of cobalt catalyst prepared by the reduction of cobalt oxide granule with hydrogen at a temperature between 250 and 450 C. The reaction was conducted at a temperature between 95 .and 110 C. for about 1 hour. 75% of the formaldehyde cyanhydrin was converted to N-dimethylethanolamine. Some higher boiling compounds were likewise obtained.

Easample 5.-The process of Example 1 by duplication using 7.7 parts of formaldehyde, 7 parts of acetone cyanhydrin, 140 parts of isobutanol and 20 parts of the nickel catalyst and conducting the reaction at a temperature of 90 to 100 C. for about 1 hour will produce N- methyl and N-dimethyl tertiary-butanolamine.

All of the processes described in the examples were carried out under a hydrogen pressure of approximately 700 atmospheres.

Optimum yields are obtained by the use of more than normal amounts of catalyst. Ordinarily, in conducting catalytic hydrogenation reaction, the catalyst is employed to the extent of about /2% up to a maximum of about by weight based on the compound to be hydrogenated. It has been found, however, in the hydrogenation and alkylation of aldehyde cyanhydrins to N-substituted alkanolamines, that there should be present a large amount of catalyst over this amount, and this is true even with the -highly active catalysts such as the nickel and cobalt catalysts described in the examples, Generally the catalyst should be present in amounts ranging from 25% to in the order of 250% or more based on the weight of aldehyde cyanhydrin present. Moreover, it has been discovered that a catalyst containing small amounts of alkali, such as are found in the Raney nickel catalyst, gives higher conversions to N-methyl diethanolamine. Those like cobalt which are al- ;kali free give higher conversions to N-dimethylethanolamine.

The process may, if desired, be carried out by way of a continuous process as distinguished from a batchwise process. By such a process the aldehyde cyanhydrin together with the aldehyde, solvent and hydrogen are introduced continuously into a reaction zone, which may, for example, be a cylindrical converter in which the ratio of diameter to length is not greater than about 1:10. The converter is charged with the catalyst and with substantially no free space at the inlet end, so that substantially immediately after the introduction of the reactants they directly contact a relatively large volume of the catalyst under the temperature and pressures of hydrogenation. This type of converter avoids undue mixin of the product with the cyanhydrins and thereby inhibits the formation of reaction prod ucts resulting from such mixtures.

I claim:

1. A process for the preparation of an N-dimethylethanolamine which comprises subjecting formaldehyde cyanhydrin to hydrogenation in the presence of formaldehyde and 4 to 20 parts. by weight of methanol per part of formaldehyde cyanhydrin at a temperature between 15 and C., a pressure between 200 and 700 atmospheres and in the presence of at least 25% 1) weight of a hydrogenation catalyst.

2. A process for the preparation of N-dimethylethanolamine which comprises subjecting formaldehyde cyanhydrin to hydrogenation in the presence of formaldehyde, from 4 to 20 parts of methanol per part by weight of formaldehyde cyanhydrin, and at least 25% of a cobalt hydro.- gsnation catalyst based on the weight of formaldehyde cyanhydrin, at a temperature between 15 and 150 C., and a pressure between 200 and 700 atmospheres.

3. A process for the preparation of N-dimethylethanolamine which comprises subjecting formaldehyde cyanhydrin to hydrogenation in the presence of formaldehyde, from 4 to 20 parts of methanol per part by weight of formaldehyde cyanhydrin and at least 25% of a Raney nickel catalyst based on the weight of formaldehyde cyanhydrin at a temperature between 15 and 150 C., and a pressure between 200 and 700 atmospheres.

WILLIAM F. GRESHAM.-

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Y Great Britain Jan. 19, 1942 

